For air-conditioning apparatuses, especially those including multiple indoor units for the purpose of air-conditioning for buildings, hotels, and the like, expansion mechanisms are arranged on the indoor units for refrigerant distribution. Such air-conditioning apparatuses easily produce refrigerant flow noise. Especially when indoor load is small, the rotation speed of an indoor fan in the indoor unit is slow. Thus, fan motor or wind noise is relatively small, and in contrast the refrigerant flow noise is the relatively main factor of noise. Since refrigerant flow noise is in a high frequency band and occurs discontinuously, there is a problem that the noise is easy to audibly recognize, therefore significantly destroying the comfortability of the room.
Regarding existing air-conditioning apparatuses, an air-conditioning apparatus is disclosed, for example, which includes a capillary tube arranged in parallel to a variable expansion mechanism, thus preventing excessive refrigerant flow caused by precision unevenness of the expansion mechanism when in small flow quantity and decreasing the occurrence of refrigerant noise (see Patent Literature 1).
Furthermore, for example, using porous transmitting materials for the internal structure of an expansion mechanism to prevent the occurrence of refrigerant flow noise and to decrease noise is disclosed (see, for example, Patent Literature 2).
Furthermore, for example, delaying the decline timing of rotation speed of the indoor fan when an indoor unit is turned off and thus avoiding noise from being audibly recognized even when refrigerant noise is present is disclosed (see, for example, Patent Literature 3).